Method of making articles with super-hydrophobic and/or self-cleaning surfaces

ABSTRACT

Super-hydrophobic and self-cleaning articles produced by imprinting exposed surfaces with suitable fine-grained and/or amorphous metallic embossing dies to transfer a dual surface structure, including ultra-fine features less than or equal to 100 nm embedded in and overlaying a surface topography with macro-surface structures greater than or equal to 1 micron are disclosed.

The present invention is a continuation of U.S. Ser. No. 12/785,662filed May 24, 2010, the disclosure of which is incorporated herein inits entirety.

FIELD OF THE INVENTION

The present invention relates to articles having exposed patternedsurfaces which, at least in part, are super-hydrophobic and/orself-cleaning. The exposed surfaces have a dual microstructure includingultra-fine features equal to or less than 100 nm embedded in andoverlaying a surface topography with macro-surface structures equal toor greater than 1 micron and are produced by intimate contact withfine-grained and/or amorphous embossing dies containing a relief patternof the same surface topography.

BACKGROUND OF THE INVENTION

The present invention generally relates to a method of suitablytexturing at least part of the exposed surface(s) of an article with adual surface structure which is inherently water repellant including,but not limited to, organic polymers optionally containing a variety ofadditives and/or fillers, by employing amorphous and/or fine-grainedmetallic embossing dies or molds exhibiting a relief pattern containinga dual surface structure.

Water repellant (hydrophobic), super-hydrophobic and self-cleaningsurfaces are desired in numerous applications involving, at least attimes, exposure to the atmosphere or water. According to the prior art,known super-hydrophobic surfaces (contact angle for water greater thanor equal to 150°) which are self-cleaning are created by introducingartificial surface structures including elevations and/or depressions ina smooth surface of an inherently hydrophobic material (contact anglefor water greater than 90°), for example, organic polymers or coatings.Suitable distances between the elevations and/or depressions arereported to be in the range of from 5 μm to 200 μm, and the heightsand/or depths of the elevations and/or depressions are in the range offrom 5 μm to 100 μm.

The prior art describes various means of increasing the water repellentproperties of hydrophobic surfaces by roughening.

U.S. Pat. No. 3,354,022 describes water repellent surfaces having anintrinsic advancing water contact angle of more than 90° and anintrinsic receding water contact angle of at least 75° by creating amicro rough structure with elevations and depressions in a hydrophobicmaterial. The high and low portions have an average distance of not morethan 1,000 microns, an average height of high portions of at least 0.5times the average distance between them. The air content is at least 60%and, in particular, fluorine containing polymers are disclosed as thehydrophobic material. The water repellent surfaces are created using anembossing die made of hollow polymer fibers. Unfortunately, suchembossing dies are cumbersome to produce and have a limited durability.

U.S. Pat. No. 6,660,363 describes self-cleaning surfaces of objects madeof hydrophobic polymers or permanently hydrophobized materials whichhave an artificial surface structure of elevations and depressions. Thedistances between the elevations are in the range of from 5 μm to 200μm, and the heights of the elevations are in the range of from 5 μm to100 μm. At least the elevations consist of hydrophobic polymers orpermanently hydrophobized materials. The elevations cannot be wetted bywater or by water containing detergents by attaching PTFE particles (7micron in diameter) to a polymer adhesive film containing surface andcuring the structure or by using a fine mesh screen to emboss a polymersurface by hot pressing. According to the '363 patent, such surfaces areproduced by application of a dispersion of powder particles of an inertmaterial in a siloxane solution, and subsequent curing the siloxanesolution to form a polysiloxane. Unfortunately, the structure formingparticles do not adhere well to the surface, are cumbersome to produce,and have a limited durability.

U.S. Patent Publication No. 2003/0187170 discloses a process forproducing nanostructured and microstructured polymer films by guidingthe polymer through a gap formed by a suitably patterned roll and ameans which develops an opposing pressure so that the polymer film isdeformed and shaped in accordance with the relief pattern. Noinformation is provided in the '170 publication to substantiate thenanostructured features disclosed or to demonstrate the wetting behaviorof the embossed polymer films.

U.S. Pat. No. 6,764,745 describes a structural member in which highwater-repellency can be obtained by forming appropriate irregularitieson the external surface. The irregularities comprise protrusion portionsof uniform height and shaped as prisms and which are subsequently coatedwith a water repellent film of PTFE or fluoroslkylsilane. The surfacefeatures termed “irregularities” have such dimensions that a waterdroplet cannot fall into the air-filled recesses. This approach requiresmultiple materials and/or layers and a final topcoat to render thearticle superhydrophobic.

U.S. Pat. No. 6,872,441 describes glass, ceramic and metal substrateswith at least one self-cleaning surface comprising a layer with amicro-rough surface structure which is arranged on the substrate andmade at least partly hydrophobic. The layer contains a glass flux andstructure-forming particles with a mean particle diameter within the 0.1to 50 micron range. The micro-rough surface structure has a ratio ofmean profile height to mean distance between adjacent profile tipswithin the 0.3 to 10 micron range. The surface layer is produced bycoating the substrate with a composition containing a glass flux andstructure-forming particles, and the layer is burnt in and madehydrophobic. This approach requires multiple materials and/or layers anda final topcoat to render the article superhydrophobic and is rathercomplex.

U.S. Ser. No. 12/785,650, entitled “METALLIC ARTICLES WITH HYDROPHOBICSURFACES”, which has a common assignee and is filed concurrently withthe present application, describes articles having exposed metallicsurfaces comprising durable, fine-grained and/or amorphousmicrostructures which, at least in part, are rendered water repellant bysuitably texturing and/or roughening the surface to increase the contactangle for fluids including water, thus reducing the wetting behavior ofthe surface, reducing corrosion and enabling efficient cleaning anddrying.

The prior art also addresses the fabrication of fine-grained and/oramorphous metallic coatings and articles for a variety of applications.

U.S. Pat. No. 3,303,111 discloses amorphous nickel phosphorus (Ni—P)and/or cobalt phosphorus (Co—P) coatings using electroless deposition.

U.S. Pat. No. 5,389,226 discloses amorphous and microcrystallineelectrodeposited nickel-tungsten (Ni—W) coatings of high hardness, wearand corrosion resistance and low residual stress to avoid cracking andlifting of the coating from the substrate.

U.S. Pat. No. 5,032,464 discloses smooth ductile alloys of a transitionmetal and phosphorus, particularly nickel phosphorus (Ni—P) with highductility (up to 10%) produced by electrodeposition.

U.S. Pat. No. 5,288,344 describes beryllium (Be)-bearing alloys whichform amorphous metallic glasses upon cooling below the glass transitiontemperature at a cooling rate appreciably less than 10⁶ K/s.

U.S. Pat. No. 7,575,040 describes a process for continuous castingamorphous metal sheets by stabilizing the molten alloy at castingtemperature, introducing the alloy onto a moving casting body, andquenching the molten alloy to solidify it.

U.S. Pat. No. 5,352,266 and U.S. Pat. No. 5,433,797, which are assignedto the same assignee, describe a process for producing nanocrystallinematerials, particularly nanocrystalline nickel. The nanocrystallinematerial is electrodeposited onto the cathode in an aqueous acidicelectrolytic cell by application of a pulsed current.

U.S Patent Publication No. 2005/0205425 and DE 10228323, both beingassigned to the same assignee as the present application, disclose aprocess for forming coatings, layers or freestanding deposits ofnanocrystalline metals, metal alloys or metal matrix composites. Theprocess employs tank plating, drum plating or selective platingprocesses using aqueous electrolytes and optionally a non-stationaryanode or cathode. Nanocrystalline metal matrix composites are disclosedas well.

U.S. Patent Publication No. 2009/0159451, which has a common assignee asthe present application, discloses graded and/or layered, variableproperty electrodeposits of fine-grained and amorphous metallicmaterials, optionally containing solid particulates.

U.S. Ser. No. 12/548,750, assigned to the same assignee as the presentapplication, discloses fine-gained and amorphous metallic materialscomprising cobalt (Co) of high strength, ductility and fatigueresistance.

U.S. Ser. No. 12/785,524, which is a continuation-in part of U.S. Ser.No. 12/476,455, entitled “METAL CLAD POLYMER ARTICLE”, and is filedconcurrently with the present application, discloses metal-clad polymerarticles comprising polymeric materials having fine-grained (averagegrain-size of 2 nm to 5,000 nm) or amorphous metallic materials ofenhanced pull-off strength between the metallic material and the polymerwhich are optionally wetproofed.

DE 10108893 describes the galvanic synthesis of fine-grained group II togroup V metals, their alloys and their semiconductors compounds usingionic liquid or molten salt electrolytes.

U.S. Pat. No. 5,302,414 describes a cold gas-dynamic spraying method forapplying a coating to an article by introducing metal or metal alloypowders, polymer powders or mixture thereof into a gas stream. The gasand particles, which form a supersonic jet having a velocity of fromabout 300 msec to about 1,200 msec, are directed against a suitablesubstrate to provide a coating thereon.

U.S. Pat. No. 6,895,795 describes a method of processing a billet ofmetallic material in a continuous manner to produce severe plasticdeformation. The billet is moved through a series of dies in oneoperation to produce a billet with a refined grain structure.

U.S. Pat. No. 5,620,537 describes a method of superplastic extrusion forfabricating complex-shaped, high strength metal alloy components bycarefully controlling strain rate and temperature to retain anultra-fine grained microstructure. A high strength, heat treatable metalalloy is first processed, such as by equal channel angular extrusion(ECAE), to have a uniform, equiaxed, ultra-fine grain size in thicksection billet form.

Thus, the prior art teaches that, in order to substantially raise thecontact angle for water, surface features need to be introduced to theexposed surface of an inherently non-wetting material as illustrated innumerous naturally occurring structures. The material has to beinherently hydrophobic and has to contain a patterned surface comprisingsuitable depressions and/or elevations as observed in lotus or aspenleaves, rose petals, etc.

Numerous attempts have been made to replicate nature as noted above toachieve super-hydrophobic and/or self-cleaning properties in man-madearticles. As indicated previously, U.S. Patent Publication No.2003/0187170 describes embossed polymer surfaces with nano-sized andmicro-sized structures by shaping/patterning the polymer surface withappropriate processes including injection molding, die embossing, orrotary embossing. The relief pattern on the forming tool can be createdby sandblasting, etching, laser ablation, lithographic techniques,offset printing, electroplating techniques, LIGA and/or erosion. The'170 publication guides towards the employ of LIGA to create formingtools with dimensions in the nanometer range (100 nm to 300 nm depth).The use of galvanoforming to generate the forming tool by plating onto anegative hollow mold of plaster, wax etc. is disclosed as well. Theworking examples illustrate the production of forming tools using LIGAwith the smallest dimension (depth) being 1,000 nm (1 micron). None ofthe working examples illustrate the generation of nano-structuredfeatures overlaying a micro-structured features as set forth in thepresent application, i.e., a dual structure composed of a primaryfeatures in the 1 μm to 1,000 μm range (i.e., a primary structure)overlayed by a secondary structure with ultra-fine features in the rangeof between 1 nm and 100 nm. The only plausible interpretation of the'170 publication suggests that the spacing and/or height/depth of themicro-structures themselves can have a dimension in the nanometer range.However, there is no teaching or suggestion in the '170 publication of adual microstructure including ultra-fine features equal to or less than100 nm embedded in and overlaying a surface topography withmacro-surface structures equal to or greater than 1 micron of thepresent application.

The '170 publication discloses the use of metallic or a polymericmaterials as an imprinting tool. The '170 publication, however, makes nodistinction with respect to the material microstructure and allinformation provided suggests to the person skilled in the art that, inthe case of using metallic imprinting rolls, conventional metallicmaterials such as steel with a coarse grained microstructure (averagegrain size greater than 30 microns) are being employed. Similarly, thegeneral electroforming techniques disclosed would produce coarse-graineddeposits. As highlighted, the only dimension in the nanometer rangedisclosed by the '170 publication is the depth of the structure whichranges over six (6) orders of magnitude, from 10 nm to 10,000,000 nm(10,000 μm). Notably, no single contact angle measurement, tilt anglemeasurement or any evidence of super-hydrophobic properties using theprocess disclosed, are provided in the '170 publication.

SUMMARY OF THE INVENTION

The Applicants have surprisingly discovered that prior art depressionsand/or elevations (hereafter termed “primary structure”) can beconveniently textured to create an overlaying ultra-fine/nanometer-sizedprofile (hereafter termed “secondary structure”) on the micrometer (μm)sized features when employing fine-grained and/or amorphous metallicembossing dies. Embossing dies or forming reliefs according to thepresent invention must contain both micrometer (μm) sizeddepressions/elevations and, in addition, an ultra-fine/nanometer-sizedpattern in order to significantly increase the contact angle ofmaterials such as polymers embossed with such dies. The Applicants havefurthermore discovered that the secondary structure is indeedtransferred from the metallic forming dies onto the embossed polymersurface, at least in part, due to the generally non-wetting propertiesof the metallic forming die itself.

The Applicants have also surprisingly discovered that the surface offine-grained and/or amorphous metallic material can readily be texturedto form desired nanostructured and microstructured features required onthe embossing die surface. The same approach does not result in the sameperformance when prior art coarse-grained metallic embossing dies areemployed which are processed the very same way.

It is therefore an objective of the present invention to provide aconvenient process which established a dual structure embossing diesurface containing a nanostructured pattern overlayed on amicrostructured surface for use to suitably imprint polymer or othermaterial surfaces, preferably in a single step, and render suchprocessed surfaces super-hydrophobic and self-cleaning.

It is an objective of the present invention to utilize durable metallicmaterials comprising an amorphous and/or fine-grained microstructure onand near the embossing die surface.

It is an objective of the present invention to suitably nano-texture andmicro-texture metallic materials comprising an amorphous and/orfine-grained microstructure for embossing of suitable materialsincluding, but not limited to, polymers, by a convenient process,preferably by a two step process comprising shot-peening followed byetching.

It is an objective of the present invention to create suitablenanostructured and microstructured metallic surfaces comprisingfine-grained and/or amorphous metallic materials for use toemboss/imprint surfaces of hydrophobic materials to raise the contactangle and/or lower the tilt angle, including, but not limited to,polymers by forming various recesses and depressions which extendinwardly from the original surface of the metallic material and/or byforming various elevations which protrude from the original surface ofthe metallic material.

It is an objective of the present invention to provide articles whereinthe wetproofed embossed material surface extends over between 1% and100% of the total exposed surface of the article.

It is an objective of the present invention to provide durable, scratchand abrasion resistant, strong, lightweight articles with at leastpartially embossed outer surfaces for use in various applications, e.g.,in transportation applications (including automotive, aerospace, shipsand other vessels navigating in and on water, and their components),defense applications, industrial components, building materials,consumer products, electronic equipment or appliances and theircomponents, sporting goods, molding applications and medicalapplications.

It is an objective of the invention to provide suitably nano-patternedand micro-patterned metallic embossing dies selected from the group ofamorphous and/or fine-grained metals, metal alloys or metal matrixcomposites. The exposed metallic layer comprises at least somefine-grained and/or amorphous metallic materials which can be producedin freestanding form or can be applied to suitable permanent substratesby a large variety of metal forming or deposition processes. Preferredmetal deposition processes which can be used to produce a microstructurewhich is fine-grained and/or amorphous are selected from the group ofelectroless deposition, electrodeposition, physical vapor deposition(PVD), chemical vapor deposition (CVD), cold spraying and gascondensation. Other metal processing techniques for rendering themicrostructure of metallic material fine grained, e.g., severe plasticdeformation, or for rendering the microstructure amorphous, e.g., rapidsolidification, are contemplated as well.

It is an objective of the present invention to provide single ormultiple structural metallic layers for use as nano-overlayed,micro-patterned embossing dies having a microstructure selected from thegroup of fine-grained, amorphous, graded and layered structures, whichhave a total thickness in the range of between 1 micron and 2.5 cm,preferably between 50 micron and 2.5 mm and more preferably between 100micron and 500 micron.

The fine-grained and/or amorphous metallic material of the embossingdies has a high yield strength (25 MPa to 2,750 MPa) and ductility (0.1%to 45%).

It is an objective of the present invention to utilize the enhancedmechanical strength and wear properties of fine-grained metalliccoatings/layers with an average grain size between 1 nm and 5,000 nm,and/or amorphous coatings/layers and/or metal matrix compositecoatings/layers as embossing dies. Metal matrix composites (MMCs) inthis context are defined as particulate matter embedded in afine-grained and/or amorphous metal matrix. MMCs can be produced, e.g.,in the case of using an electroless plating or electroplating process,by suspending particles in a suitable plating bath and incorporatingparticulate matter into the deposit by inclusion or, e.g., in the caseof cold spraying, by adding non-deformable particulates to the powderfeed.

It is an objective of the present invention to suitably texture at leastportions of the metallic surfaces to form a large number of micron-sizedfeatures including at least one of recesses, protrusions and elevationstermed “micron-sized surface structures” or “micron-sized surface sites”per unit area. Recesses can be formed by suitably removing material fromthe smooth surface, while elevations can be formed by suitably texturinga mold surface and applying the fine grained and/or amorphous metallicmaterial to the mold surface, e.g., by electroless or electrodeposition,followed by removal of the metallic layer from the mold.

It is an objective of the present invention to optionally coat thesuitable patterned and textured metallic embossing dies surface byapplying a top coat comprising a metallic, ceramic or organic coating ortransfer it onto a secondary embossing dies to change the structuresfrom protrusions to recesses or vice-versa.

It is an objective of the present invention to suitably create numerouspits and crevices or protrusions in at least portions of the outersurface of the metallic embossing dies that are randomly and/or evenlydistributed which form the primary structure of the relief patternsurface used for embossing. The shape, size and population of sites suchas recesses, pits, crevices, depressions and the like is believed toenable the entrapment of air thus providing for the “lotus” or “petal”effect observed in nature. It is an objective to create micro-sizedsurface structures exceeding a density of between 25 and 10,000 sitesper mm² area, preferably between 100 and 5,000 sites per mm² area or arange of between 5 and 100 sites per mm. Surface sites range from 5-100micron in depth, preferably 10-50 micron in depth; from 5-100 micron indiameter, preferably from 10-50 micron in diameter, spaced between 5-100micron apart, preferably between 10 and 50 micron apart.

It is an objective of the present invention to suitably overlay theprimary surface features with an ultra-fine pattern of secondary surfacefeatures which can be conveniently created using metallic materials forembossing dies having a fine-grained and/or amorphous microstructure asillustrated.

It is an objective of the present invention to render inherentlyhydrophobic surfaces super-hydrophobic (contact angle for water greaterthan 150°) and self-cleaning (tilt angle less than 5°) by introducingsurface structures therein containing a plurality of micron-sizedfeatures, wherein the plurality of micron-sized features furthermorepreferably has a substructure comprising of a plurality of nanoscalefeatures, i.e., the surface sites contain both micro and nanostructuredfeatures.

It is an objective of the invention to suitably create metallic surfacehaving a low roll-off angle (tilt angle for water less than 25°),preferably a self-cleaning surface having tilt angle for water less than5°), and/or high contact angle for water (contact angle greater than125°) by an economic, convenient and reproducible process.

It is an objective of the present invention to apply suitably structuredfine-grained and/or amorphous metallic relief forms to at least aportion of the surface of a part made or being made substantially of anysuitable material, including, but not limited to polymers, compositesand ceramics, suitably modifying at least portions of said outer surfacein contact with the relief form to render it hydrophobic.

It is an objective of the present invention to provide lightweightarticles comprising, at least in part, liquid repellent and/orself-cleaning outer surfaces with increased wear, erosion and abrasionresistance, durability, strength, stiffness, thermal conductivity andthermal cycling capability.

It is an objective of the present invention to provide articles with atleast in part liquid repellent and/or self-cleaning outer surfaces for avariety of applications including, but not limited to:

-   -   (i) applications requiring cylindrical objects including gun        barrels; shafts, tubes, pipes and rods; golf and arrow shafts;        skiing and hiking poles; various drive shafts; fishing poles;        baseball bats, bicycle frames, ammunition casings, wires and        cables and other cylindrical or tubular structures for use in        commercial goods;    -   (ii) medical equipment including orthopedic prosthesis and        surgical tools crutches, wheel chairs and medical equipment        including orthopedic prosthesis, implants and surgical tools;    -   (iii) sporting goods including golf shafts, heads and        faceplates; lacrosse sticks; hockey sticks; skis and snowboards        as well as their components including bindings; racquets for        tennis, squash, badminton; bicycle parts;    -   (iv) components and housings for electronic equipment including        laptops; televisions and handheld devices including cell phones;        personal digital assistants (PDAs) devices; walkmen; discmen;        digital audio player, e.g., MP3 players; e-mail functional        telephones, e.g., a BlackBerry®-type device; cameras and other        image recording devices;    -   (v) automotive components including heat shields; cabin        components including seat parts, steering wheel and armature        parts; fluid conduits including air ducts, fuel rails,        turbocharger components, oil, transmission and brake parts,        fluid tanks and housings including oil and transmission pans;        cylinder head covers; spoilers; grill-guards and running boards;        brake, transmission, clutch, steering and suspension parts;        brackets and pedals; muffler components; wheels; brackets;        vehicle frames; spoilers; fluid pumps such as fuel, coolant, oil        and transmission pumps and their components; housing and tank        components such as oil, transmission or other fluid pans        including gas tanks; electrical and engine covers;    -   (vi) industrial/consumer products and parts including linings on        hydraulic actuator, cylinders and the like; drills; files; saws;        blades for knives, turbines and windmills; sharpening devices        and other cutting, polishing and grinding tools; housings;        frames; hinges; sputtering targets; antennas as well as        electromagnetic interference (EMI) shields;    -   (vii) molds and molding tools and equipment;    -   (viii) aerospace parts and components including wings; wing        parts including flaps and access covers; structural spars and        ribs; propellers; rotors; rotor blades; rudders; covers;        housings; fuselage parts; nose cones; landing gear; lightweight        cabin parts; cryogenic storage tanks; ducts and interior panels;        and    -   (ix) military products including ammunition, armor as well as        firearm components, and the like; that are coated with        fine-grained and/or amorphous metallic layers that are stiff,        lightweight, resistant to abrasion, resistant to permanent        deformation, do not splinter when cracked or broken and are able        to withstand thermal cycling without degradation.

Accordingly, the invention in one exemplary embodiment is directed to anarticle comprising an outer surface comprising a polymeric material withat least a portion thereof having a dual surface microstructure havingone of a contact angle for water at room temperature greater than orequal to 130° and a tilt angle for water at room temperature less thanor equal to 25°. The dual surface microstructure of the portion of thearticle outer surface comprises a primary surface structure and asecondary surface structure at least partially overlaying the primarysurface structure. The primary surface structure has surface featureshaving dimensions and a spacing between adjacent primary surfacefeatures in the range of 1 micron to 1,000 microns. The secondarysurface structure has surface features having dimensions and a spacingbetween adjacent secondary surface features in the range of 1 nm to lessthan or equal to 100 nm.

Accordingly, the invention in another exemplary embodiment is directedto an article formed of a polymeric material comprising an outer surfacewith at least a portion thereof having a dual surface microstructure.The dual surface microstructure of the outer surface portion includingultra-fine surface features having dimensions less than or equal to 100nm embedded in and overlaying macro-surface features having dimensionsgreater than 1 micron. The dual surface microstructure raises thecontact angle in the outer surface portion by at least 35° and decreasesthe tilt angle in the outer surface portion by at least 10° fordeionized water at room temperature when compared to a smooth outersurface portion of the article of the same composition.

Accordingly, the invention in yet another exemplary embodiment isdirected to a method for manufacturing an article formed of a polymericmaterial and having one of a hydrophobic and self-cleaning outersurface. The method for manufacturing comprises the steps of:

-   -   (i) providing an embossing die formed of a metallic material,        the metallic material having at least one of a microstructure        which is fine-grained with an average grain size between 2 and        5,000 nm and an amorphous microstructure;    -   (ii) incorporating surface structures into at least an exposed        surface portion of the embossing die, the surface structures        increasing the contact angle for water at room temperature to        over 90° and rendering the inherently hydrophilic surface of the        metallic material hydrophobic; and    -   (iii) imprinting at least a portion of an outer surface of the        article with the imprinted surface portion of the embossing die        to at least one of increase the contact angle for water at room        temperature of said outer surface portion to at least 130° and        decrease the tilt angle for water at room temperature of said        outer surface portion to less than or equal to 25°.

According to exemplary embodiments of the present invention, a methodfor manufacturing an article having an exposed (outer or inner) surface,comprising at least portions that are rendered wetting resistant,hydrophobic and/or self-cleaning, is disclosed. A wetting-resistantsurface, in the most common embodiment, exhibits resistance to wettingby water. However, the use of other liquids including organic liquidssuch as, for example, alcohols and the like, are contemplated as well.Unless otherwise indicted, the liquid is deionized water.

As used herein, the term “contact angle” or “static contact angle” isreferred to as the angle between a static drop of deionized water and aflat and horizontal surface upon which the droplet is placed.

As is well known in the art the contact angle is used as a measure ofthe wetting behavior of a surface. If a liquid spreads completely on thesurface and forms a film, the contact angle is zero degrees (0°). As thecontact angle increases, the wetting resistance increases, up to atheoretical maximum of 180°, where the liquid forms spherical drops onthe surface. The term “wet-proof” is used to describe surfaces having ahigh wetting resistance to a particular reference liquid; “hydrophobic”is a term used to describe a wetting resistant surface where thereference liquid is water. As used herein, the term “wetproof” and“hydrophobic” refers to a surface that generates a contact angle ofgreater than 90° with a reference liquid. As the wetting behaviordepends in part upon the surface tension of the reference liquid, agiven surface may have a different wetting resistance (and hence form adifferent contact angle) for different liquids. As used herein, the term“substrate” is not construed to be limited to any shape or size, as itmay be a layer of material, multiple layers or a block having at leastone surface of which the wetting resistance is to be modified.

As used herein the “inherent contact angle” or “intrinsic contact angle”is characterized by the contact angle for a liquid measured on a flatand smooth surface not containing any surface structures. Unlessotherwise indicted, the liquid is deionized water.

As used herein the term “smooth surface” is characterized by a surfaceroughness (Ra) less than or equal to 0.25 microns.

As used herein the term “hydrophilic” is characterized by the contactangle for water of less than 90°, which means that the water dropletwets the surface.

As used herein the term “hydrophobic” is characterized by the contactangle for water of greater than 90°, which means that the water dropletdoes not wet the surface.

As used herein, “super-hydrophobicity” refers to a contact angle fordeionized water at room temperature equal to or greater than 150° and“self-cleaning” refers to a tilt angle of equal to or less than 5°.

As used herein the term “lotus effect” is a naturally occurring effectfirst observed on lotus leaves and is characterized by having a randomlyrough surface and low contact angle hysteresis, which means that thewater droplet is not able to wet the microstructure spaces between thespikes. This allows air to remain inside the texture, causing aheterogeneous surface composed of both air and solid. As a result, theadhesive force between the water and the solid surface is extremely low,allowing the water to roll off easily and to provide the “self-cleaning”phenomena.

As used herein the term “petal effect” is based on microstructures andnanostructures observed on rose petals. These structures are larger inscale than the lotus leaf, which allows the liquid film to impregnatethe texture. While the liquid can enter the larger scale grooves, itcannot enter into the smaller grooves. Since the liquid can wet thelarger scale grooves, the adhesive force between the water and solid isvery high. The water drops maintain their spherical shape due to thehydrophobicity of the petal (contact angle of 152°). This explains whythe water droplet will not fall off even if the petal is tilted at anangle or turned upside down.

As used herein, the term “tilt angle” or “roll-off angle” means thesmallest angle between a surface containing a water droplet and thehorizontal surface at which the droplet commences to and keeps rollingoff.

As used herein, the term “coating” means deposit layer applied to partor all of an exposed surface of a substrate.

As used herein, the term “coating thickness” or “layer thickness” refersto depth in a deposit direction and typical thicknesses exceed 50micron, preferably 100 micron to accommodate the height/depth of thesurface features required to obtain the lotus or petal effect.

As used herein, “exposed surface” and “outer surface” refer to allaccessible surface area of an object accessible to a liquid. The“exposed surface area” refers to the summation of all the areas of anarticle accessible to a liquid.

As used herein, the term “surface structures” or “surface sites” refersto surface features including recesses, pits, crevices, dents,depressions, elevations, protrusions and the like purposely created inthe metallic material to decrease its wetability and increase thecontact angle.

As used herein, the term “population of primary surface structures”refers to number of primary, micron-sized, surface features per unitlength or unit area. The “linear population of surface structures” canbe obtained by counting the number of structures, e.g., on a crosssectional image and normalizing it per unit length, e.g., per mm. Theaverage “areal population of surface structures” is the square of theaverage linear population, e.g., expressed in cm² or mm². Alternatively,the average areal density can be obtained by counting the number offeatures visible in an optical micrograph, SEM image or the like andnormalizing the count for the measurement area.

As used herein, “surface roughness”, “surface texture” and “surfacetopography” mean a regular and/or an irregular surface topographycontaining surface structures. Surface roughness consists of surfaceirregularities which result from the various surface preconditioningmethods used such as mechanical abrasion and etching to create suitablesurface structures. These surface irregularities/surface structurescombine to form the “surface texture” presumably retaining air and arebelieved to be responsible for the increase in contact angle whencompared to a flat surface, particularly, when these features alsocontain sub-texturing or secondary texturing on the nanoscale, i.e.,below 100 nm.

According to one aspect of the present invention, a super-hydrophobicand/or self-cleaning polymeric article is provided by embossing apolymer with a fine-grained and/or amorphous metallic die bycompression, injection molding or embossing. The fine-grained and/oramorphous metallic die can be produced by a number of processes, ashighlighted in detail in co-pending application entitled “METALLICARTICLES WITH HYDROPHOBIC SURFACES”. Preferably, a convenient andeconomic process is employed, e.g., electrodeposition, which generallycomprises the steps of (i) positioning the metallic or metallized workpiece to be plated in a plating tank containing a suitable electrolyteand a fluid circulation system, (ii) providing electrical connections tothe work piece/cathode to be plated and to one or several anodes, and(iii) plating a structural layer of a metallic material with an averagegrain size of equal to or less than 5,000 nm and/or an amorphousmicrostructure.

If the desired relief form is not engraved into or otherwise embedded inthe surface of the cathode used as a work piece for theelectrodeposition it can be added afterwards. In this case theappropriate surface structures in the electrodeposited mold surface aregenerated on at least portions of the metallic surface, e.g., byapplying at least one process selected from the group of mechanicalabrasion, shot-peening, anodic dissolution, anodic assisted chemicaletching, chemical etching and plasma etching. Other applicable methodsinclude, but are not limited to, micro-machining and nano-machining,micro-stamping, micro-profiling and laser ablation. A particularlypreferable and economic process entails the application of shot-peeningfollowed by etching.

It is understood that the use of such processes, while generallymodifying the surface, does not inadvertently yield a suitable moldcapable of rendering the embossed polymer super-hydrophobic andself-cleaning and that not each and every process under each and everyarbitrary process condition will yield the desired increase in contactangle in the embossed material surface. The Applicants found that theprocess sequence of processing steps and process parameters had to besuitably adjusted and optimized to achieve the desired population anddimensions of surface sites to yield the desired liquid repellency inthe embossed polymer surface. For example, in the case of usingshot-peening, depending on the hardness of the surface to be modified,the Applicants found that the peening media hardness and size, thepeening pressure and the peening duration had to be optimized to achievethe surface structures required for raising the contact angle.Similarly, the Applicants found that, for example, in the case ofetching, depending on the chemical composition of the surface, theetching media, process temperature and duration had to be optimized toestablish the surface sites required for raising the contact angle.

Suitable embossing dies comprise a single or several fine-grained and/oramorphous metallic layers as well as multi-layer laminates composed ofalternating layers of fine-grained and/or amorphous metallic layerswhich are free standing or are applied as coatings to at least a portionof a suitable substrate.

The fine-grained metallic coatings/layers of suitable embossing dieshave a grain size under 5 μm (5,000 nm), preferably in the range of 2 nmto 1,000 nm, more preferably between 10 nm and 500 nm. The grain sizecan be uniform throughout the deposit; alternatively, embossing dies canconsist of layers with different microstructure/grain size. Amorphousmicrostructures and mixed amorphous/fine-grained microstructures arewithin the scope of the invention as well.

The fine-grained and/or amorphous embossing dies can containparticulates dispersed therein, i.e., they can be metal matrixcomposites (MMCs). The particulates can be permanently retained withinthe metal matrix and/or they can be chosen to be soluble in the etchantto further enhance the desired size and population of surface structurescontributing to the rise in contact angle in the metallic material aswell as in the embossed surfaces.

According to the present invention, the entire surface of the embossedarticle can be imprinted with the super-hydrophobic and/or self-cleaningsurface features; alternatively, patches or sections can be formed onselected areas of the article, e.g., selected sections or sectionsparticularly prone to heavy use and/or exposure to water in all of itsforms, i.e., accumulations of sea or fresh water, rain, hail, snow, ice,or wet surfaces such as consumer and sporting goods, automotive andaerospace components and the like.

The following listing further defines the exemplary fine-grained and/oramorphous metallic embossing die material used for practicing theinvention:

Metallic Coating/Metallic Layer Specification

Metallic materials comprising at least one element selected from thegroup consisting of Ag, Al, Au, Co, Cr, Cu, Fe, Ni, Mo, Pb, Pd, Pt, Rh,Ru, Sn, Ti, W, Zn and Zr. Other alloying additions optionally comprisingat least one element selected from the group consisting of B, C, H, O, Pand S.

Particulate additions optionally comprising at least one materialselected from the group consisting of: metals and metal oxides selectedfrom the group consisting of Ag, Al, In, Mg, Si, Sn, Pt, Ti, V, W, Zn;carbides and nitrides, including, but not limited to, Al, B, Cr, Bi, Si,W; carbon (carbon nanotubes, diamond, graphite, graphite fibers); glass;and self lubricating materials including, but not limited to, MoS₂,polymer materials (PTFE, PVC, PE, PP, ABS, epoxy resins). Particulateadditions are preferably in the form of powders, fibers, nanotubes,flakes, and the like.

Microstructure: Amorphous or crystalline Minimum average grain size[nm]: 2; 5; 10 Maximum average grain size [nm]: 100; 500; 1,000; 5,000;10,000 Metallic layer Thickness Minimum [μm]: 1; 10; 25; 30; 50; 100Metallic layer Thickness Maximum [mm]: 1; 5; 25 Minimum particulateparticle size [μm]: 0.01; 0.1 Maximum particulate particle size [μm]: 5,10 Minimum particulate fraction [% by 0; 1; 5; 10 volume]: Maximumparticulate fraction [% by 50; 75; 95 volume]: Minimum Yield StrengthRange [MPa]: 100; 300 Maximum Yield Strength Range [MPa]: 2,750 MinimumHardness [VHN]: 50; 100; 200; 400 Maximum Hardness [VHN]: 800; 1,000;2,000 Minimum contact angle on smooth surface 0, 25, 50, <90, <95, <100for deionized water at room temperature [°]: Maximum contact angle onsmooth surface 160, 180 for deionized water at room temperature [°]:

Wetproofed (Textured) Embossed Layer Surface Specification

Minimum contact angle of textured surface ≧125; ≧130, ≧140 for deionizedwater at room temperature [°]: Maximum contact angle on textured surface160, 180 for deionized water at room temperature [°]: Minimum increasein contact angle for 40, 50 deionized water at room temperature of theembossed surface when compared to the flat and smooth surface of thesame composition [°]: Maximum contact angle for deionized water 60, 70,90 at room temperature of the embossed surface when compared to the flatand smooth surface of the same composition [°]: Minimum linearpopulation of micron-sized 5, 10 (primary) surface structures [numberper mm]: Maximum linear population of micron-sized 100; 1,000 (primary)surface structures [number per mm]: Minimum areal population ofmicron-sized 10, 25, 100 (primary) surface sites [number per mm²]:Maximum areal population of micron-sized 5,000; 10⁵; 10⁶ (primary)surface sites [number per mm²]: Minimum micron-sized (primary) surface1, 5, 10 structure diameter, spacing or depth [μm]: Maximum micron-sized(primary) surface 50, 100, 250, 1000 structure diameter, spacing ordepth [μm]: Minimum micron-sized (secondary) surface 1, 5 structurediameter, spacing or depth [nm]: Maximum micron-sized (secondary)surface 75, 90, 95, 100 structure diameter, spacing or depth [nm]:Surface structure topography: recesses; cavities; pitted surfacestructures; holes; pores; depressions; grooved, roughened and etchedsurface sites; or open foam type structures; “brain”, “cauliflower”,“worm”, “coral”, elevations, protrusions and other three dimensionallyinterconnected porous surface structures

Typically any number of different surface structures is present in thesuitably textured surface, their shapes and areal densities can beirregular and the clear identification of individual surface structurescan, at times, be subject to interpretation.

Embossed Layer Substrate Specification

Polymeric materials comprise at least one of: unfilled or filled epoxy,phenolic or melamine resins, polyester resins, urea resins;thermoplastic polymers such as thermoplastic polyolefins (TPOs)including polyethylene (PE) and polypropylene (PP); polyamides, mineralfilled polyamide resin composites; polyphthalamides, polyphtalates,polystyrene, polysulfone, polyimides; neoprenes; polybutadienes;polyisoprenes; butadiene-styrene copolymers; poly-ether-ether-ketone(PEEK); polycarbonates; polyesters; liquid crystal polymers such aspartially crystalline aromatic polyesters based on p-hydroxybenzoic acidand related monomers; polycarbonates; acrylonitrile-butadiene-styrene(ABS); chlorinated polymers such polyvinyl chloride (PVC); andfluorinated polymers such as polytetrafluoroethylene (PTFE). Polymerscan be crystalline, semi-crystalline or amorphous.

Filler additions: metals (Ag, Al, In, Mg, Si, Sn, Pt, Ti, V, W, Zn);metal oxides (Ag₂O, Al₂O₃, SiO₂, SnO₂, TiO₂, ZnO); carbides of B, Cr,Bi, Si, W; carbon (carbon, carbon fibers, carbon nanotubes, diamond,graphite, graphite fibers); glass; glass fibers; fiberglass metallizedfibers such as metal coated glass fibers; mineral/ceramic fillers suchas talc, calcium silicate, silica, calcium carbonate, alumina, titaniumdioxide, ferrite, mica and mixed silicates (e.g. bentonite or pumice).

Minimum particulate/fiber fraction [% by volume]: 0; 1; 5; 10

Maximum particulate/fiber fraction [% by volume]: 50; 75; 95

Surface structures generated with selected processes described hereininclude sandblasting and etching typically which are inexpensive andyield a somewhat random distribution of surface sites. Regularly spacedand sized surface sites of defined shape and uniform size can be createdby micromachining (e.g., laser scribing, laser ablation and micro- andnano-machining) or LIGA processes to a preform, followed by depositionof the fine-grained and/or amorphous material into these “moldpreforms”, followed by removal of the fine-grained and/or amorphousmetallic layer from the preform molds. As also indicated, the micronsized recesses preferably further contain an additional substructure,e.g., sub-micron sized structures as observed in lotus leaves or rosepetals, which can be conveniently created in the relief form by, e.g.,shot-peening and etching. Therefore determining the average size, andlinear or areal density of such sites to achieve the desiredhydrophobicity is at times challenging. In light of these challenges,for the purpose of the present invention, one reliable method thereforeto characterize such surfaces is to measure their contact angle forwater at room temperature which was observed to be a reliable andreproducible property.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary process showing each exemplary processstep to form a relief form and create a hydrophobic surface in asuitable polymer using the relief form according to one of theembodiments of the present invention.

FIG. 2 illustrates a micrograph of a modified surface of coarse-grainednickel (Ni) (average grain size: 30 μm) after shot-peening and chemicaletching illustrating the appearance of the treated surface at lowmagnification in FIG. 2 a and a high magnification in FIG. 2 b. Thefigures reveal the lack of a dual-scale surface roughness.

FIG. 3 illustrates a micrograph of modified surface of fine-grainednickel (Ni) (average grain size: 15 nm) after shot-peening and chemicaletching illustrating the dual-scale surface roughness at lowmagnification in FIG. 3 a and a high magnification in FIG. 3 b.

FIG. 4 illustrates a micrograph of a polypropylene sheet embossed withthe relief pattern of the embossing die as illustrated in FIG. 3 toillustrate that the primary and the secondary surface structures wereindeed transferred from the metallic embossing die onto the polymersurface. The modified polypropylene surface containing the dual-scalesurface roughness is illustrated at low magnification in FIG. 4 a and ahigh magnification in FIG. 4 b.

DETAILED DESCRIPTION

The present invention relates to embossing the surface of hydrophobicmaterials, preferably polymeric materials, to render their exposed outersurface super-hydrophobic and/or self-cleaning. The metallicfine-grained and/or amorphous embossing dies are produced by a number ofconvenient processes including, but not limited to, DC or pulseelectrodeposition, electroless deposition, physical vapor deposition(PVD), chemical vapor deposition (CVD) and gas condensation or the like.Other processing techniques for forming the desired microstructureinclude, but are not limited to, rapid solidification and severe plasticdeformation. The required surface structures are created by a number ofconventional processes ranging from micromachining to shot-peeningfollowed by etching.

The person skilled in the art of plating will know how to electroplateor electroless plate selected fine-grained and/or amorphous metals,alloys or metal matrix composites choosing suitable plating bathformulations and plating conditions. Similarly, the person skilled inthe art of PVD, CVD, gas condensation, severe plastic deformation andrapid solidification techniques will know how to prepare fine-grainedand/or amorphous metal, alloy or metal matrix composite coatings.

The Applicants have surprisingly discovered that the microstructure ofthe metallic material significantly affects the performance of theembossing dies and fine-grained and/or amorphous metallic embossing diesare superior to conventional metals having a coarse grainedmicrostructure.

As highlighted, optionally, the patterned metallic embossing die surfacecan be at least partly subjected to a suitable finishing treatment,which can include, among others, electroplating, i.e., chromium platingand applying a polymeric material.

Numerous attempts have been made to identify, characterize and quantifydesired surface structures which result in achieving the desired wettingproperties in embossed polymers and to quantify the surface topographyand surface roughness in quantifiable scientific terms. Heretofore,these efforts have not succeeded in part because of the complexity ofthe surface features and the numerous parameters such as population,size and shape of the surface structures which affect the contact angle.Furthermore, the polymer surface can be at least partially oxidized by asuitable chemical and/or heat treatment or surface oxidation occursnaturally with time.

According to the present invention, surface structures containing thedesired dual-scale roughness in the polymeric articles are suitablycreated by intimate contact with the embossing die surface as can beachieved by compression molding, injection molding, polymer casting orany other suitable polymer casting, shaping or processing method asdescribed in detail in copending application entitled “METALLIC ARTICLESWITH HYDROPHOBIC SURFACES,” U.S. Ser. No. 12/785,650.

Combinations of two or more of the aforementioned processes can be usedas well and the specific treatment conditions typically need to beoptimized to maximize the change in contact angle. As highlighted,fine-grained and/or amorphous metals which are shot-peened followed byetching produce particularly suitable embossing dies.

Articles and parts suitably embossed with the appropriate dies include avariety of materials, preferrably polymeric substances. Suitablepolymeric substrates include crystalline, semi-crystalline and/oramorphous resins as well as unfilled or filled resins. Suitablepolymeric substrates include epoxy, phenolic and melamine resins,polyester resins, urea resins; thermoplastic polymers such asthermoplastic polyolefins (TPOs) including polyethylene (PE) andpolypropylene (PP); polyamides, including aliphatic and aromaticpolyamides, mineral filled polyamide resin composites; polyphthalamides;polyphtalates, polystyrene, polysulfone, polyimides; neoprenes;polybutadienes; polyisoprenes; butadiene-styrene copolymers;poly-ether-ether-ketone (PEEK); polycarbonates; polyesters; liquidcrystal polymers such as partially crystalline aromatic polyesters basedon p-hydroxybenzoic acid and related monomers; polycarbonates;acrylonitrile-butadiene-styrene (ABS); chlorinated polymers suchpolyvinyl chloride (PVC); and fluorinated polymers such aspolytetrafluoroethylene (PTFE). Useful thermoplastic resins includepoly(oxymethylene) and its copolymers; polyesters such as poly (ethyleneterephthalate), poly (1,4-butylene terephthalate), poly(1,4-cyclohexyldimethylene terephthalate), and poly(1,3-propyleneterephthalate); polyamides such as nylon-6,6, nylon-6,nylon-12, nylon-11, nylon-10,10, and aromatic-aliphatic copolyamides;polyolefins such as polyethylene (i.e., all forms such as low density,linear low density, high density, etc.), polypropylene, polystyrene,polystyrene/poly (phenylene oxide) blends, polycarbonates such as poly(bisphenol-A carbonate); fluoropolymers including perfluoropolymers andpartially fluorinated polymers such as copolymers of tetrafluoroethyleneand hexafluoropropylene, poly (vinyl fluoride), and the copolymers ofethylene and vinylidene fluoride or vinyl fluoride; poly-sulfides suchas poly (p-phenylenesulfide); polyetherketones such as poly(ether-ketones), poly (ether-ether-ketones), and poly(ether-ketone-ketones); poly (etherimides);acrylonitrile-1,3-butadinene-styrene copolymers; thermoplastic (meth)acrylic polymers such as poly (methyl methacrylate); and chlorinatedpolymers such as poly (vinyl chloride), polyimides, polyamideimides,vinyl chloride copolymer, and poly (vinylidene chloride). Useful“thermotropic liquid crystalline polymer” (LCP) include polyesters, poly(ester-amides), and poly (ester-imides). One preferred form of polymeris “all aromatic”, that is all of the groups in the polymer main chainare aromatic (except for the linking groups such as ester groups), butside groups which are not aromatic may be present. The thermoplasticsmay be formed into parts by the usual methods, such as injectionmolding, thermoforming, compression molding, extrusion, and the like.

These polymeric articles frequently contain fillers including carbon,carbon nanotubes, graphite, graphite fibers, carbon fibers, metals,metal alloys, glass and glass fibers; fiberglass, metallized fibers suchas metal coated glass fibers; pigments, dyes, stabilizers, tougheningagents, nucleating agents, antioxidants, flame retardants, process aids,and adhesion promoters and the like. Appropriate filler additions in thesubstrate range from as low as 2.5% per volume or weight to as high as95% per volume or weight. In addition to fibrous reinforcing fillerswith a high aspect ratio, other fillers such as glass, ceramics andmineral fillers such as talc, calcium silicate, silica, calciumcarbonate, alumina, titanium dioxide, ferrite, and mixed silicates (e.g.bentonite or pumice) can be employed as well.

Particularly suitable polymer composites include carbon/graphite fiberand glass fiber resin composites in which the resin components includephenolic resins, epoxy resins, polyester resins, urea resins, melamineresins, polyimide resins, polyamide resins as well as elastomers such asnatural rubber, polybutadienes, polyisoprenes, butadiene-styrenecopolymers, polyurethanes, and thermoplastics such as polyethylene,polypropylene, and the like.

Suitable super-hydrophobic and/or self-cleaning articles processedaccording to the present invention include, but are not limited to,parts used in aerospace, automotive, building material and otherindustrial applications. Carbon/graphite-fiber polymer composites are apopular choice for lightweight aerospace components including planefuselage, wings, rotors, propellers and their components as well asother external structures that are prone to erosion by the elementsincluding wind, rain, hail and snow.

The following working example illustrates the benefits of the invention,reporting the static contact angle and tilt angle for water of smoothpolymers, as well as embossed polyethylene using dies with variousmicrostructures specifically for fine-grained, coarse-grained andamorphous metallic embossing dies

WORKING EXAMPLE Comparison of Contact Angle and Tilt Angle ofPolyethylene Imprinted with Various Coarse-Grained, Fine-Grained andAmorphous Embossing Dies

In this example, 10 cm×10 cm×0.25 mm metallic embossing dies were madefrom three different materials, namely, (a) coarse-grained Ni with anaverage gain size of 30 microns (prior art); (b) fine-grained Ni with anaverage gain size of 15 nm (this invention); and (c) amorphous Co-9P(this invention). Coarse-grained Ni was procured from McMaster-Carr(Aurora, Ohio, USA) in the form of cold rolled & annealed metal sheet.Fine-grained Ni and amorphous Co—P sheets were prepared according toU.S. Pat. No. 5,352,266, and copending application U.S. Ser. No.12/785,520. The sheets are available from Integran Technologies Inc.(www.integran.com; Toronto, Canada), the assignee of the presentapplication. Fine-grained metal matrix coupons and amorphous couponswere electroformed as described in U.S. Patent Publication No.2005/0205425, also available from Integran Technologies Inc.

To achieve a reproducible and comparable surface the metal surface ofeach sample to be used for the embossing die was initially ground flatup to 2400 grit SiC paper, rinsed in ethanol, ultrasonically cleaned inethanol and air dried at room temperature. To eliminate any potentialcontamination, no polishing compounds were employed.

Embossing dies were prepared from the coarse-grained, fine-grained, oramorphous metal sheet as follows:

-   -   (i) No further surface preparation;    -   (ii) Chemical etching: etching was performed in 5% HNO₃ for        about 30 min at room temperature. Following the etching, samples        were rinsed in deionized water and submerged in suitable        neutralizing solution, rinsed again and then ultrasonically        cleaned in ethanol and air dried at room temperature;    -   (iii) Shot-peening: shot-peening was performed at about 87 psi        (about 10 passes) using 180 grit alumina media at a distance of        about 10 cm, followed by rinsing in ethanol, ultrasonic cleaning        in ethanol, followed by air drying at room temperature;    -   (iv) Process (ii) followed by process (iii), i.e., etching        followed by shot-peening; and    -   (v) Process (iii) followed by process (ii), i.e., shot-peening        followed by etching.

The fifteen relief forms (five each for the three differentmicrostructures) were used to emboss 10×10 cm polypropylene plaquesprocured from McMaster-Carr (Aurora, Ohio, USA) by hot-pressing at about160° C. After processing, the contact angle of the all processedpolyethylene surfaces was measured. In all cases, the contact angle wasmeasured by placing multiple 5 μl droplets of deionized water on theflat sample surface and taking a picture with a stereoscope at 15×magnification after properly aligning the camera with the horizontalplane of the sample. Contact angle measurements were taken from thedigitally captured images using the Image-pro software in triplicates onboth sides of each droplet. In all cases the average of all contactangle measurements is reported.

The contact angle and tilt angle measurements for polypropyleneimprinted with a variety of dies is displayed in Table 1. The dataillustrates a dramatic difference in contact angles and tilt angledepending on the microstructure and the surface processing employed onthe metallic embossing die. The data illustrate thatsuper-hydrophobicity and self-cleaning properties can not be achievedusing coarse-grained embossing dies. In the case of fine-grained and/oramorphous metallic dies, super-hydrophobicity and self-cleaningproperties were achieved only if the die surface processing involvedshot-peening followed by chemical etching according to the exemplaryprocess highlighted in FIG. 1 generating the dual-scale surfacestructures.

TABLE 1 Contact Angles and Tilt Angles of Polyethylene Sheets Embossedwith Coarse-Grained, Fine-Grained and Amorphous Embossing DiesContaining Various Surface Structures. Die Microstructure Coarse-grainedNi Dies Fine-Grained Ni Amorphous Co—9P (Prior Art) Dies Dies ContactTilt Contact Tilt Contact Tilt Polypropylene Angle Angle Angle AngleAngle Angle Surface: [degrees] [degrees] [degrees] [degrees] [degrees][degrees] Smooth Surface 93 38 93 38 93 38 Embossed with Die 104 27 9925 96 30 with Etched Surface Embossed with Die 119 31 130 24 135 23 withShot Peened Surface Embossed with Die 131 30 139 22 124 39 with SurfaceEtched followed by Shot- Peening Embossed with Die 122 30 151 <5 153 <5with Surface Shot- Peened followed by Etching

FIG. 1 schematically illustrates the exemplary process described above.As shown, the exemplary embossing die has a microstructure which isfine-grained with an average grain size between 2 nm and 5,000 nm. Asindicated previously, the embossing die can also have an amorphousmicrostructure. The embossing die has at least an exposed surfaceportion having structures incorporated therein by, for example,shot-peening followed by etching. The surface structures can have a dualmicrostructure. Particularly, according to one aspect, the surfacestructures include a primary surface structure and a secondary surfacestructure which at least partially overlays the primary surfacestructure. The primary surface structure has macro-features in the rangeof 1 μm to 1,000 μm and secondary surface structure has ultra-finefeatures in the range of 1 nm to 100 nm. As shown, the primary andsecondary surface features can include, for example, elevations,depressions, pits, crevices, cavities, and the like. The embossing diehaving the relief form is then used to emboss a polymer. This results inthe exposed surface of the polymer having the same dual microstructureas the embossing die, which, in turn, provides a polymer article havinga contact angle and tilt angle for water at room temperature set forthin Table 1 above.

FIGS. 2 through 3 illustrate the prevailing surface structures generatedon selected nickel (Ni) dies. Specifically, FIG. 2 illustrates amicrograph of modified surface of polycrystalline nickel (Ni) (averagegrain size: 30 μm) after shot-peening (10 passes at 87 psi with 180 gritalumina at a distance of 10 cm) and chemical etching (5% HNO3 @ roomtemperature for about 30 minutes) at low magnification in FIG. 2 a and ahigh magnification in FIG. 2 b, illustrating the lack of a dual-scalesurface roughness.

FIG. 3 illustrates the fine-grained nickel (Ni) surface after theshot-peened surface (10 passes at 87 psi with 180 grit alumina at adistance of 10 cm) has been exposed to a chemical etching treatment (5%HNO3 @ room temperature for about 30 minutes). Specifically, FIG. 3 aindicates the spherical depression with a diameter ranging from 10microns to 50 microns generated, presumably as the sites struck by thealumina shot act as local corrosion sites promoting etching. FIG. 3 b isa much higher magnification image of the very same surface focusing inon a depression, revealing the secondary roughness with features visiblefrom less than 1 micron to about 5 microns. Further magnification(TEM/not shown) visualizes a number of features much below 100 nm insize. A dramatic difference in surface morphology is visible whencomparing the processed coarse-grained surface of FIG. 2 with thefine-grained nickel (Ni) surface of FIG. 3 explaining the observeddifferences in contact angles when used as embossing dies.

FIG. 4 illustrates the polyethylene surface after embossing with thefine-grained nickel (Ni) surface of FIG. 3. Specifically FIG. 4 aindicates the spherical protrusions generated by the embossing die witha diameter ranging from 10 microns to 50 microns generated and FIG. 4 bis a much higher magnification image of the very same surface focusingin on a the edge of the protrusion, indicating the secondary roughnesswith features visible from less than 1 micron to about 5 microns hasbeen successfully transferred from the embossing die to the polymersurface. Again further magnification (TEM/not shown) illustrates thatthe very small features (much below 100 nm in size) observed on theembossing dies are transferred as well.

Table 1 above indicates that the contact angle on polyethylene usingprior art, coarse-grained dies can be ultimately increased from 93° to131° (38° increase), whereas in the case of fine-grained dies thecontact angle is ultimately increased from 93° to 151° (58° increase),and in the case of amorphous dies the contact angle is ultimatelyincreased from 93° to 153° (60° increase). Similarly the tilt angle/rolloff angle of the embossed polyethylene is affected as well, namely inthe case of coarse-grained dies the tilt angle is ultimately loweredfrom 38° to 27° (11° decrease), whereas in the case of fine-grained andamorphous dies the tilt angles are ultimately lowered from 38° to lessthan 5° (greater than 33° decrease). Table 1 also indicates that onlypolyethylene plaques embossed with fine-grained or amorphous dies thathave been shot-peened, followed by etching achieved super-hydrophobicityand self-cleaning behavior.

Similar results have been obtained by using other metallic materialcompositions for embossing dies and when imprinting other polymersincluding filled and unfilled polyamides, ABS, PTFE and polypropylenes.

The foregoing description of the invention has been presented describingcertain operable and preferred embodiments. It is not intended that theinvention should be so limited since variations and modificationsthereof will be obvious to those skilled in the art, all of which arewithin the spirit and scope of the invention.

1. A method for manufacturing an article formed of a polymeric materialand having at least one of a hydrophobic and a self-cleaning outersurface, the method for manufacturing comprising the steps of: (i)providing an embossing die having an exposed surface portion formed of ametallic material, the metallic material having at least one of afine-grained microstructure with an average grain size between 2 and5,000 nm and an amorphous microstructure, a smooth surface of themetallic material being inherently hydrophilic at room temperature, thesmooth surface has a surface roughness less than or equal to 0.25microns; (ii) incorporating surface structures into the exposed surfaceportion of the embossing die to define a textured surface portion of theembossing die, said textured surface portion rendering the inherentlyhydrophilic smooth surface of the metallic material at room temperaturehydrophobic; and (iii) imprinting at least a portion of the outersurface of the polymeric material of the article directly with thetextured surface portion of the embossing die.
 2. The method accordingto claim 1, wherein the imprinting step increases the contact angle forwater at room temperature of the outer surface portion of the polymericmaterial to at least 125° and/or decreases the tilt angle for water atroom temperature of said outer surface portion of the polymeric materialto less than or equal to 25°.
 3. The method according to claim 1,wherein the metallic material has a fine-grained microstructure.
 4. Themethod according to claim 1, wherein the metallic material has anamorphous microstructure.
 5. The method according to claim 1, whereinthe metallic material is a multi-layer laminate.
 6. The method accordingto claim 1, wherein the metallic material is free standing or applied asa coating to at least a portion of a substrate.
 7. The method accordingto claim 1, wherein the fine-grained and/or amorphous microstructure ofthe metallic material is made by a process selected from electrolessdeposition, electrodeposition, physical vapor deposition, chemical vapordeposition, cold spraying and gas condensation.
 8. The method accordingto claim 1, wherein the outer surface portion of the article comprisesrandomly distributed surface structures containing a plurality ofmicron-sized features, wherein the plurality of micron-sized featuresfurther has a substructure comprising of a plurality of nanoscalefeatures.
 9. The method according to claim 1, wherein the exposedmetallic material surface portion is treated by at least one processselected from the group consisting of chemical etching, electrochemicaletching, plasma etching, shot-peening, grinding, and machining.
 10. Themethod according to claim 1, wherein the exposed metallic materialsurface portion is treated by shot-peening followed by etching.
 11. Themethod according to claim 1, wherein said metallic material is selectedfrom the group of: (i) one or more metals selected from the groupconsisting of Ag, Al, Au, Co, Cr, Cu, Fe, Ni, Mo, Pd, Pt, Rh, Ru, Sn, TiW, Zn and Zr, (ii) pure metals or alloys containing at least two of themetals listed in (i), further containing at least one element selectedfrom the group of B, C, H, O, P and S; (iii) any of (i) or (ii) wheresaid metallic coating also contains particulate additions in the volumefraction between 0 and 95% by volume.
 12. The method according to claim11, wherein the metallic material contains particulate addition of atleast 1% by volume and said particulate addition is of one or morematerials selected from the group consisting of a metal, a metal oxide,a carbide, a polymer material, ceramic, glass and a carbon selected fromthe group consisting of carbon nanotubes, diamond, graphite, andgraphite fibers.
 13. The method according to claim 1, further comprisingincorporating dual-roughness surface structures into the exposedmetallic material surface portion of the embossing die.
 14. The methodaccording to claim 13, wherein the dual-roughness surface structurescomprise a primary surface structure and a secondary surface structureat least partially overlaying said primary surface structure, theprimary surface structure including surface features having dimensionsand a spacing between adjacent primary surface features in the range of1 micron to 1,000 microns, and the secondary surface structure includingsurface features having dimensions and a spacing between adjacentsecondary surface features in the range of 1 nm to less than or equal to100 nm.
 15. The method according to claim 1, wherein said embossing diecomprises at least one metallic material selected from the groupconsisting of Ni, Co, P, Cu and Fe.
 16. The method according to claim 1,wherein said polymeric material comprises a material selected from thegroup consisting of unfilled or filled epoxies, phenolic or melamineresins, polyester resins, urea resins, thermoplastic polymers,polyamides, mineral filled polyamide resin composites, polyphthalamides,polyphtalates, polystyrene, polysulfone, polyimides, neoprenes,polybutadienes, polyisoprenes, butadiene-styrene copolymers,poly-ether-ether-ketone (PEEK), polycarbonates, polyesters, liquidcrystal polymers, polycarbonates, acrylonitrile-butadiene-styrene (ABS),chlorinated polymers, and fluorinated polymers.
 17. A method formanufacturing an article formed of a polymeric material and having atleast one of a hydrophobic and a self-cleaning outer surface, the methodfor manufacturing comprising the steps of: (i) providing an embossingdie formed of a metallic material, the metallic material having at leastone of a microstructure which is fine-grained with an average grain sizebetween 2 and 5,000 nm and an amorphous microstructure; (ii)incorporating surface structures into at least an exposed metallicmaterial surface portion of the embossing die to define a texturedsurface portion by first shot-peening the metallic material surface andfollowed by etching the metallic material surface, the textured surfaceportion rendering the at room temperature inherently hydrophilic surfaceof the smooth surface portion of the metallic material surface having asurface roughness (Ra) less than or equal to 0.25 microns at roomtemperature hydrophobic; and (iii) imprinting at least a portion of anouter surface of the polymeric material of the article directly with thetextured metallic material surface portion of the embossing die.
 18. Themethod according to claim 17, wherein the imprinting step increases thecontact angle for water at room temperature of said outer surfaceportion of the polymeric material to at least 125° and/or decreases thetilt angle for water at room temperature of said outer surface portionof the polymeric material to less than or equal to 25°.
 19. The methodaccording to claim 17, further comprising incorporating dual-roughnesssurface structures into the exposed metallic material surface portion ofthe embossing die, wherein the dual-roughness surface structurescomprise primary surface structures and secondary surface structures atleast partially overlaying said primary surface structures, and a linearpopulation of said primary surface structures is in the range of 5 to1000 per mm.
 20. The method according to claim 17, wherein the metallicmaterial has a fine-grained microstructure.
 21. The method according toclaim 17, wherein the metallic material has an amorphous microstructure.22. The method according to claim 17, wherein the metallic material is amulti-layer laminate.
 23. The method according to claim 17, wherein themetallic material is free standing or applied as a coating to at least aportion of a substrate.